This invention relates to a machine for thermally treating and sterilizing pre-packaged food articles by means of microwaves, being of a type which comprises a treatment tunnel provided with an inlet port and an outlet port, a conveyor extending longitudinally of the tunnel interior between said ports to convey packages of said food articles laid in parallel rows, at least one microwave generator within said tunnel, and microwave radiators arranged to face said rows.
Machine of this general type are currently widely employed in the industry to carry out thermal treatments accompanied by sterilization on pre-packaged food articles prepared on a commercial scale for subsequent distribution and retail sale, possibly in the frozen form.
The microwave treatment carried on such machines, while being in more than one way advantageous and generally more effective than traditional thermal treatment methods, has nevertheless the drawback specified herein below.
Where, for example, the articles are contained in trays orderly laid in parallel longitudinal rows on a pan-like carrier, lack of uniformity is encountered in the temperature, along a normal direction to the direction of advance of the articles on the conveyor belt. In other words, all the trays which occupy the same position in succession are subjected to the same thermal treatment, but trays in different rows have temperatures which differ from one another.
This brings about a serious problem in that an effective sterilization of the article is impaired which can only be achieved if a predetermined temperature can be held stable for a prearranged time period.
Furthermore, it cannot be postulated of obviating this drawback by an increase in the energy radiated in the treatment tunnel, to thus increase the average treatment temperature, because due to the very disuniformity in the temperatures reached some articles might undergo excessive heating and become burned locally.